In MB money it's about ~£200 for A Service and double that for B Service.
Indie would be about half the above, depending on who's doing it.
But MB tends to discount servicing for cars older than 4 years, so phone around.
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Also, keep in mind that A and B Services are only oil service with additional checks - and depending on age and mileage there may be additional work needed such as brake fluid change, air and/or fuel filter change, transmission fluid change, etc etc, all of which will be charged separately (not to mention brake discs/pads if needed) so check what's needed exactly and how much it will cost before booking the car for service.